Method of manufacturing selenium rectifiers



METHOD OF MANUFACTURING SELENIUM RECTIFIERS Eric Lionel French, London, England, asslgnor to Westinghouse Brake and Signal Company, Limited, London, England No Drawing. Original application June 7, 1956, Serial No. 589,878, now PatentNo. 2,828,453, dated March 25, 1958. Divided and this application January 2,

1958, Serial No. 706,555

22 Claims.- (Cl. 117-200) My invention relates to a method of manufacturing selenium cells for rectifiers of the kind in which an artificial or non-genetic barrier layer is provided between the selenium and counter-electrode layers.

This application is a division of my copending application Serial No. 589,878, filed June 7, 1956, and now United States Patent Patent No. 2,828,453, for Selenium Rectifiers and assigned to the assignee of my present application.

According to the invention, in a rectifier of the kind described the non-genetic layer includes or consists of solid ethoxylene resin.

. The term ethoxylene resinmeans, in this specification, an aliphatic aromatic polyether with terminal epoxy groups and pendant hydroxyl groups such, for example, as that produced by the alkaline condensation of epichlor hydrin and 2,2'-bis(4-hydroxy phenyl) propane. The term solid ethoxylene resin means a resin of this kind which is solid at 80 C. and is to be understood as in cluding an ethoxylene resin havingpendant hydroxyl groups which is produced from an ethoxylene resin of lower molecular weight by curing: it is, further to be understood that the ethoxylene resin of lower molecular weight may be liquid at 80 C.

The effect of introducing the ethoxylene resin is to increase the reverse resistance of the rectifier. When the non-genetic layer includes a material other than the solid ethoxylene resin that other material may be a diluent, such as polyvinyl chloride, which has the eifect of diminishing progressively as its proportion is increased the effect of the ethoxylene resin upon the reverse resistance of the rectifier. Alternately, that other material may be D-glucose, which, when present as a discrete layer adjacent to the ethoxylene resin has the effect of enhancing the influence of the ethoxylene resin upon the reverse resistance of the rectifier.

Alternatively that other material may be a curing agent for the ethoxylene resin, an excess of which may be preseat as a discrete layer adjacent to the ethoxylene resin after curing is complete. Suitable curing agents are low molecular weight linear polyamides containing reactive amine groups such as are prepared by reacting a polyfunctional aliphatic amine and a dimeric fatty acid, for

example, that sold under the trade name Beckalide 10. Alternatively the curing agent may be a monofunctional amine which reacts with the terminal epoxy groups of the ethoxylene resin to produce an amine alcohol such, for example, as piperidine. Alternatively also, the curing agent may be a polyfunctional amine which reacts with the terminal epoxy groups of the ethoxylene resin to produce a cross-linked structure such, for example, as triethylene tetramine. Alternatively, also, that other material maybe a linear polyhydroxy compound which is solid at room temperature and which reacts by etherification of the terminal epoxy groups of the ethoxylene resin, such as an acyclicl linear polyhedric alcohol of which sorbitol is one example.

.According to one method ofputting the invention into effect an incomplete rectifier element consisting of a base 2,875,103 Patented Feb. 24, 1959 ICC plate having a layer of selenium applied to it, the selenium being in its crystalline form, is immersed for one minute in a 6% solution by weight of ethoxylene resin of the kind sold under the trade name Epikote 1009 dissolved in a xylene-benzyl alcohol solvent mixture, the plate being arranged with its plane vertical and being withdrawn vertically at a rate of six inches per minute. The temperature at which this dipping is performed is so chosen that the solvent mixture evaporates almost completely and the plate is dry in appearance within a few seconds of its being withdrawn from the solution. As, however, benzyl alcohol has a deleterious effect upon the degree of electroforming which may be achieved, its complete removal is desirable. To this end, the plate is preferably exposed to radiant heat for a few minutes immediately after its withdrawal from the solution. The counter-electrode is then applied and the element is electroformed in known manner.

Alternatively, the ethoxylene resin sold under the trade name Epikote 1007" may be used instead of the Epikote 1009 referred to above.

Other solvents may be used in place of the benzyl alcohol referred to above, for instance, methyl ethyl V with the benzyl alcohol solvent, they may be diluted with an aromatic hydrocarbon such as xylene, the proportion of aromatic hydrocarbon being adjusted to give a rate of evaporation such that the plate is dry in appearance within a fewfseconds of its being withdrawn from the solution. Exposure of the plate to radiant heat after its withdrawal from the solution is desirable also when these other solvents are used. To some degree the reverse resistance of the rectifier is dependent upon the particular solvent used, the higher alcohols, for instance benzyl alcohol, giving particularly good results.

The rate of evaporation also. depends upon ambient temperature and rate of air flow past the plate. The procedure set out above has been found suitable for a xylene-benzyl alcohol solvent mixture containing parts by weight of xylene and 25 parts by weight of benzyl alcohol, used in a room which is at a temperature of 25 C. and which has a normal degree of ventilation, the resulting rectifier having a non-genetic layer of such a thickness that the forward resistance of the rectifier is of a reasonable value. Variation of any of the conditions results in a change in this forward resistance, but in practice, it has been foundconvenient, when a change in the forward resistance is desired, to change the concentration of the solution and to maintain all other conditions constant. In practice, the concentration of the solution may, for a 75/25 xylene-benzyl alcohol mixture, be conveniently varied between 1 and 10 percent. With a 1 percent solution the effect of the process upon the reverse resistance of the rectifier. be comes seriously impaired, probably because the layer becomes too thin, and at a proportion of 10 percent the effect ofincreasing this proportion becomes insignificant. The effects of variation of these other conditions are complex, but are similar to those well known in the art of forming paint films.

The stability of the completed rectifier is dependent upon the curing agent used and increases with increasing molecular weight of the ethoxylene resin present in the non-genetic layer of the completed rectifier. It is, therefore, advantageous to increase the molecular weight of the resin as far as possible by curing but the process must be performed with care because the production of resin of very high molecular weight limits the degree of electroforming which is attainable and the completion of curing prevents electroforming completely. The

reverse resistance of a rectifier the non-genetic layer of which has been cured maybe markedly higher than that of a rectifier the non-geneticlayer of which has not been cured and this increase is particularly large when trieth-ylene tetramine is used as a curing agent.

The curing agents used must be substances of the kind set out above which react mainly with the terminal ethoxylene groups.

If polyamide resins are used the use of ester solvents should be avoided as they tend to react with the curing agent and prevent curing.

Preferably the curing agent is added to the dipping solution-described above. If amines are used the proportion of curing agent may be as high as one part by weight of amine to ten parts of weight of ethoxylene resin and if polyamide resins are used the proportion may be as high as equal parts by weight. The maximum proportions suggested will ensure that the curing agent and ethoxylene resin are present in at least stoichiometric proportions in the non-genetic layer. These proportions are not, however critical and will be dependent upon the ethoxylene resin and curing agent used. Using Epikote 1009 and Beckalide the preferred proportion is 13 parts by weight of Beckalide 10 to 100 parts by weight of Epikote 1009.

Although curing proceeds continuously from the time the curing agent is added, a large number of satisfactory rectifiers may be made one after the other using the same solution, the properties of the rectifiers varying continuously, depending upon the degree of cureexisting at the time of dipping. If the curing is allowed to proceed too'far, however, electroforming is reduced and eventually prevented. Further, with certain solvents, the ethoxylene resin becomes insoluble during curing and is consequently, precipitated from the solution. It is preferable, therefore, to stabilize the solution before dipping is commenced. This may be done by adding a smaller quantity of curing agent than that suggested above, preferably half, and heating the solution until all of the curing agent has become combined with the resin. If the curing agent used is volatile the precaution must be taken of refluxing during this heating.

An alternative method of applying curing agent is .to dip a plate towhich the ethoxylene resin has been applied in asolution of thecuring agent. The solvent for the curing agent must be one which does not dissolve the ethoxylene resin to any serious degree; for cxample,.a suitable solvent for Beckalide 10 is isopropyl alcohol butif used alone it would dissolve the ethoxylene resin completely. By diluting isopropyl alcohol with acetone, however, the dipping may be performed at a temperature which is low enough to prevent serious attack upon Epikote 1009 by the isopropyl alcohol but which is high enough to ensure the substantially complete evaporation of the solvent mixture within a short time .of the plate being withdrawn from the solution.

The period during which the plate is immersed in the solution of the curing agent and the time occupied by the solvent in evaporating must be kept short in order to prevent the curing agent penetrating to the selenium in significant quantities and thereby causing an unduly high forward resistance. Using Beckalide 10-dissolved in isopropyl alcohol-acetone solvent mixture it has'been found preferable to use a solution containing 2% by weight of curing agent, the solution being maintained at 70 C., the plate being immersed for one minute and being withdrawn vertically=at a rate of six inches per minute. With other solvents it may be preferable to vary these conditions within the limits imposed by the need to limit theseverity of the attack by the curing agent upon the selenium.

As a further precaution and in order to ensure that all solvent is removed'from the plate" it is preferable to heat theq'platefor five minutes at 80 CL-immediately after its removal from "the: solution of curing agent. This has the additional effect of partially curing the ethoxylene resin but it does not effect a complete cure and so does not materially reduce the degree of electro-forming which may be attained.

Alternatively, the curing agent may be applied by a separate dipping process after, instead of before, the counterelectrode has been applied.

Curing agents having a lower reactivity than Beckalide 10 may, alternatively, be applied as a separate dip before the ethoxylene resin is applied. In order, however, to reduce the attack upon the selenium and, consequently, to reduce forward aging the time of immersion "should be reduced to a few seconds and the succeeding steps completed as rapidly as possible until the stage is reached when the rectifier is completely cured. Althougha rectifier made by this process is useful it is not possible to avoid a substantial degree of forward aging.

If a curing agent is used it is possible to make satisfactory rectifiers using as starting materials ethoxylene resins whichare liquid at C. such, for example, as that sold under the trade name Epikote 1001. The curing so increases the melting point that goo-d electroformihg is possible .and the non-genetic layer is solid at SO'ZTC. after completion of the curing.

The process of electroforrning causes heating of .the non-genetic layer and, if a curing agent is .present .inthc layer and the layer is, as it should be at the commencement of the process of electroforming, incompletely cured, this heating will cause curing to continue at a rapid rate. This curing is preferably permitted to continueuntil .all the curing agent :has been reacted with the cthoxylerie resin and if electroforming alone does not ac'hievekthis result the plate is preferably heated after electroforming until the curing is complete. In order to ensure that this may be done' theethoxylene resin ,must be present in excess,-but where there is an excess of curing agent, as there maybe if the curingagent has been applied .asa separate layer, such excess curing agent will remain after curing-has been completed.

if an amine is used as the curing agent it acts, by virtue of its alkaline nature, as aforming agent, increasing the degree of electroformingattainable. Thistreatment with an alkaline substance results, as is well-known, in an initial increase in the forward resistanceof the rectifier and a further, continuous, increase during life. Such increase in forward resistance during life maybe limited to negligible proportions by curing, whereby the amine is caused to be completely reacted with the resin.

Again, if an amine is used as the curing agent, the volatility may be such thatit can heapplied to the resin in the form of a vapor. The process may be performed by immersing the platein abeaker containing asmall quantity of the amine, the latter being sufficiently volatile at normal room temperature to prod11.e inlthe .vessel a sufficient concentration of vapor. ,Theprocessmaybe performed either before or after the counterelectrode has beenapplied. Ifthe counterelectrode has already been applied the plate iszpreferably subjected to an electroforming process immediately it is exposed to the amine vapor. The heat generated during forming increases the vaporization of the amine and at thesame time curesthe ethoxylene resin.

During the application of the. ethoxylene resinthe base plate necessarily becomes covered but the coveringisslo thin that its resistanceis small and so does not give the rectifier an unreasonably high forward resistance.

Another method ofputting the invention intoeifectis to provide a non-geneticlayer consisting offa discrete layer of solid ethoxylene-resin and a'discrete layerof D.-glucps.e, the layers being in contact with v.cach other. "This/iatrangement-gives the surprising result that the degree of electroforming issubstantially greater than that attainw able withaInon-genetic layercopsisting of ethoxylene resin alone. Preferably the ethoxylene resin" layer i s e o'ntiguouswithytheselenium layer but the positions hf mares layers" within the non-genetic layer'niay, alternatively, be reversed. i t

"In puttingthis method into eifect an incomplete rectifier element consisting of a base plate having a layer of selenium applied to it, the selenium being in its crystalline form, is immersed for one minute in a one percent solution by weightof the monosaccharide D-glucose in water, the solution being maintained at 80 C. In order to ensure uniformityof the non-genetic layer there is added to the solution amaterial which wets the selenium, for example, gelatine. The plate is then removed from the solution, being arranged with its plane vertical and being withdrawn. vertically at a rate of six inches per minute. The temperature at which this dipping is performed and the rate of withdrawal are so chosen that the water evaporates almost completely and the place is dry in appearance within a few seconds of its being withdrawn from the solution. The proportion of D-glucose may be varied within limits: with a proportion of 0.5 percent on the etfect of the processupon the rectifierbecomes seriously impaired, probably because the layer becomes too thin, and at a proportion of 4 percent the effect of increasing the proportion becomes insignificant. The proportion of wetting agent is preferably as small as possible compatible with the deposition of a uniform film. Gelatine is preferably added in the proportion of 0.02 percent by weight of'the solution and it has the unexpected eifect of pro ducing a higher reverse resistance than is obtained when using such wetting agents as that soldunder the trade name"Toepol. I i t h In order to ensure; complete evaporation of the water the plate ispreferably exposed to radiant heat for a few minutes after its withdrawal from the solution. The rate of evaporation depends, as it does when the ethoxylene resin is applied, upon the ambient temperature' and the rate of air flow past the plate whilst it is being withdrawn from the solution. The procedure set out above has been foundsuitable for use in a room ata temperature of 15 C. and having a normal degree of ventilation, the resulting rectifier having a non-genetic layer of sucha thickness that the forward resistance of the rectifier is of reasonable value. Variation in any of the conditions results in a change of this forward resistancebut, inpractica it has been found convenient to vary the thickness .of the layer by variation in the concentration of the solution, all other conditions being maintained constant.

After the platehas dried completely the counterelectrode is applied and the element electroforrned in known manner.

7. "During the application of the D-glucose the base plate necessarily becomes covered with a film of this material, in addition to the film of ethoxylene resin which has already been applied but the film is so thin that its resistance is small and the forward resistance is not increased unduly.

If the glucose layer is deposited upon the ethoxylene resin the adhesion between the glucose and the counterelectrode is poor but may be improved by heating at 110 C. to 125 C. for one to four hours after completion of the electroforming. t

In yet another method of putting the invention into effect the glucose may be replaced by a linear polyhydroxy compound which is solid at room temperature and which reacts by etherification of the terminal epoxy groups of the ethoxylene resin. Acyclic linear polyhedric alcohols are compounds of this kind and one example of such an alcohol is sorbitol.

Sorbitol may be applied in the same manner and under the same conditions as are described above in relation to the application of D-glucose. The resulting rectifier has a reverse resistance higher than that of a rectifier which is similar apart from the fact that the non-genetic layer consists of ethoxylene resin alone.

Preferably the ethoxylene resin is applied in the mannerfirst described above and a layer of so rbit ol' is applied over the ethoxylene resin. The rectifier is pref erably heated after electroforming in order to improve the adhesion between the non-genetic layer and the counterelectrode, the conditions under which the rectifier is heated being the same as those for a rectifier having a glucose layer adjacent to thecounterelectrode.

Alternatively another polyhedric alcohol may be used in place of sorbitol and as a further alternative a mixture of polyhedric alcohols may be used. When such a mixture is used the total proportion of polyhedric alcohol present in the solution is preferably the same as that present when only one such alcohol is used.

Although I have herein described several methods of forming a non-genetic or artificial barrier layer on the selenium'layer of a rectifier cell, it is to be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is; 1. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene resin.

2. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the sele-. nium layer adhering to a base plate by applying to the selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene resin to form a nongenetic layer, the ethoxylene resin being dissolved in benzyl alcohol. i

3. In a method of manufacturing selenium cells, the

step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene having pendant hydroxyl groups and which is produced by reacting an ethoxylene resin of lower molecular weight with a curing agent.

4. In' a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the seleniumlayer a solution containing between 1 and 10 percent by weight of ethoxylene having pendant hydroxyi groups and produced by reacting an ethoxylene resin of lower molecular weight with a linear polyamide containing terminal amine groups.

5. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying tothe selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene having pendant hydroxyl groups and produced by reacting an ethoxylene resin of lower molecular weight with a curing agent prepared by reacting a polyfunctional aliphatic amine and a dimeric fatty acid.

6. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene having pendant hydroxyl groups and produced by reacting an ethoxylene resin of lower molecular weight with a monofunctional amine which reacts with the terminal epoxy groups of ethoxylene resins to produce an amine alcohol.

7. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene having pendant hydroxyl groups and produced by reacting an ethoxylene resin of lower molecular weight with piperidine.

8. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the selenium 7 layr.."a., 1 n qntei i seb tween 11 a slat lne em l s t thoxylene h v ng. entlantthydr yl eens a id, r by r in nst rq ne resinqf lowe melecular weight with a polyfunetiqnal amine which re acts with the terminal .epoxy groups of the ethoxylene resin to producea cross-linked structure. g

9. In a meth d of manufacturing selenium cells, the step of forming a non-genetic barrier, layer onthe selenium layer adhering to a base plate by a'pplying to the selenium layer a solution containing between 1 and percent by weight of ethoxylene havingpendant hydroxyl groups and produced by reacting an ethoxylene resin of lower molecular weight with triethylene tetramine. I e 10. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a baseplate by applying to the selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene produced by reacting an ethoxylene resin with a linear polyhydroxy compound which, is solid at room temperature and which reacts by etherification of the terminal epoxy groups'of the ethoxylene resin. a g p l 11. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the selenium layer a solution containing between 1 and ,10 percent by weight of ethoxylene produced by reacting an ethoxylene resin with an acyclic linear polyhedric alcohol. .4

'12. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene produced by reacting an ethoxylene resin with sorbitol, c

13. In a method of manufacturing selenium cells, the step of forming a non-genetic barrier lay er 011 the se1enium layer adhering to a base plate by applying to the selenium layer a solution containing between 1 and 10 percent by weight of ethoxylene resin, and then applying a solution containing 0.5 to 4.0 percent by weight of a linear polyhydroxy compound in water to which is added just sufiicient gelatine to secure the deposition of a uniform film on the selenium layer.

14. In a method of manufacturing selenium cells, the steps of forming a non-genetic barrier layer on the selenium layer adhering to a base plate by applying to the selenium layer a layer of ethoxylene resin, and then applying a solution containing 0.5 to 4.0 percent by Weight of D-glucose in Water.

15. In a method of manufacturing selenium cells, the steps of forming a non-genetic barrier layer on the sclen layer adh ng... a besenla e hr-applyi g t th selenium layer a layer of ethoxylene resin, and thenap; p yi sa solution con a n n (1- o .Q.pe.r nt.by: we of D-glueose in water to which, is added just sufficient gelatine to secure the deposition of a uniform filmon the selenium layer.

/ 16. In a method of manufacturing selenium cells, ,the steps of forming a non-genetic barrier layer on" the selenium layer adhering to a base plate by applying alayer of ethoxylene resinto the selenium layer, and then ap plyingacuring agent. 1 7. In a method of manufacturing selenium Cells; ,the steps of forming a non-genetic .barrier layerr.on thesele nium layer adheringto a base plate by applyinga layer of ethoXylene resin to the selenium layer, andthenl'a pe plying a linear polyamide containing terminal amine s o 18. In a method of manufacturing selenium-cells, the steps of forming a non-genetic barrier layer on theyselenium layer adheringto a base plate byapplying a layer 9f ethoxylene resin to the selenium layer, and "then-111p! plying a curing agent prepared by reacting apolyfune. tional aliphatic amine and a dimeric fatty acid. 19. In a method of manufacturing selenium cells", the steps of forming a non-genetic barrierlayer on the stale nium layer adhering to a base plate by applyingga layer of ethoxylene resin to the selenium layer, and then applying amonofunctionalatnine v 20. In a method of manufacturing selenium-cells; the steps of forming a non-genetic barrier layer; on the-selenium. layer adhering to a baseplate by applying a. layer of ethoirylene resin to the selenium layer, and then applying piperidine. H V 21. In a method of manufacturing selenium cells,the steps of forming a non-genetic barrier layer. on the-sale: nium layer adhering to a base plate by applying .a layer of ethoxylene resin to theseleniumlayer, and then applyingapolyfunctional amine. x

2 2. In a method of manufacturing seleniumcells, the steps of forming a non-genetic barrier layer ontheselenium layer adhering to a base plate byapplyinga layer of ethoxylene resin to the selenium layer, and then applying triethylene tetramine.

References Cited in the fileof B UNITED STATES PATENTS v j 2,828,453 French .M'ar. '25,' 195.8. 

1. IN A METHOD OF MANUFACTURING SELENIUM CELLS, THE STEP OF FORMING A NON-GENETIC BARRIER LAYER ON THE SELENIUM LAYER ADHERING TO A BASE PLATE BY APPLYING TO THE SELENIU, LAYER A SOLUTION CONTAINING BETWEEN 1 AND 10 PERCENT BY WEIGHT OF ETHOXYLENE RESIN. 